Types of Telescopes: How do they work? and more

Telescopes originally focused light using curved, crystalline pieces of glass called lenses. However, most telescopes today use curved mirrors to collect light from the night sky. Through this article you can know the types of telescopes.

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What is a Telescope? 

The first theories of the Universe were limited by the lack of telescopes, many of the discoveries of modern astronomy would never have been made were it not for Galileo Galilei's discovery. Pirates and sea captains carried some of the earliest telescopes: they were simple glasses that only magnified your vision about four times and had a very narrow field of view.

Today's telescopes are huge arrays that can see entire quadrants of space. Galileo could never have imagined what he had set in motion.

Galileo's first telescopes were simple arrays of glass lenses that only magnified to a power of eight, but in less than two years he had improved his invention to 30 telescopes that allowed him to see the Planet Jupiter, his discovery is the basis of the modern refracting telescope.

There are two basic types of optical telescopes: Reflector and Refractor, both of which amplify distant light, but in different ways. Modern astronomers have a wide range of telescopes to use, there are optical observing platforms all over the world.

Besides those, there are radio telescopes, space telescopes and so on, each one has a specific purpose within astronomy, everything you need to know about telescopes is in the links below, including how to build your own simple telescope.

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Telescope Features

All instruments, in any configuration, are characterized by two fundamental parameters:

  • El diameter The target is indicated by the letter D and is expressed in millimeters.
  • La focal distance it is indicated by the letter F and is also expressed in mm.

The diameter

The objective diameter is the primary mirror and in turn the most important feature of the telescope, because most of the optical properties of this tool depend on it. The bigger it is, the more magnification it usually has and allows you to look at distant stars.

The diameter is usually expressed in millimeters for commercial instruments, sometimes in inches (1" = 25,4 mm). Contrary to what beginners think, a large-diameter telescope is not enough to make a good observing instrument, many other conditions related to quality and stability must be met.

Focal distance

It can be the focal length of the primary mirror or that of the eyepieces, the focal length of the instrument itself corresponds to that of the objective and is expressed in millimeters or must be calculated from the f / D ratio.

Magnification, sometimes called magnifying power, is determined by dividing the focal length of the objective by the focal length of the eyepiece. For example, if the objective lens has a focal length of 254 inches and the eyepiece has a focal length of 100 inch, then the magnification will be 2.54.

focal ratio

This is the "speed" of a telescope's optics, found by dividing the focal length by the aperture. The smaller the f-number, the lower the magnification, the wider the field, and the brighter the image with any eyepiece or camera.

Fast focal ratios of f/4 to f/5 are generally better for lower power wide-field viewing and deep space photography. Slow focal ratios of f/11 to f/15 are typically more suitable for higher power lunar, planetary and binary stargazing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint object spread out in deep space in a quarter of the time of an f/10 system, but the image will be only half the size. However, point sources, such as Stars, are recorded based on aperture, rather than focal ratio, so the larger the aperture, the fainter the star you can see or photograph, regardless of focal ratio.

How does a telescope work?

A telescope makes objects that are far away appear closer by enlarging the image formed by your eye. To understand how a telescope does this requires some background.

They allow us to see beyond; they are able to collect and focus more light from distant objects than our eyes alone, this is achieved by refracting or reflecting light using lenses or mirrors, refractive telescopes contain lenses much like those found in our own eyes, but much larger .

Inside the telescope, light first reaches a primary lens, the primary lenses are convex, rounded and can bend the captured light and aim it at a focusing secondary lens, this second lens is responsible for focusing that light to produce a clear image of the object. . 

Reflecting telescopes work similarly to refractors, but by reflecting, rather than bending, light with curved mirrors, in both cases more light captured in the primary stage means more power to see far and a more efficient focusing stage. produces clearer images.

Telescope Types

There are three main types of optical telescopes and they differ in the way they collect light to form an image:

The Refracting Telescopes

They have a curved lens at one end that focuses light down a long tube onto a second lens, called an eyepiece, which magnifies the image.

When a wave such as light passes from one medium to another at an angle, it changes direction, this is called refraction. A lens is a piece of glass designed to bend the light passing through it in such a way that an image can be produced. This type of telescope uses a series of different lens mixtures in order to create an image of an object in the distance, for example, a star or a satellite.

Reflecting Telescopes

They use mirrors instead of lenses to collect light. In a reflector, light travels down the telescope tube to the large primary mirror, which reflects the light to the smaller secondary mirror, which in turn reflects the light back to the eyepiece. Because light is reflected back and forth in reflecting telescopes, they are shorter than refracting telescopes, where light travels in a simple, straight path from one end of the telescope tube to the other.

Reflecting telescopes have other benefits over refractors, such as not being dominated by chromatic error because the radiated light does not spread according to wavelength. Similarly, the telescope duct of a reflector is shorter than that of a refractor of the same line, which minimizes the cost of the duct.

For this reason, the arc of the telescope where a reflector is located is much smaller, cheaper and easier to build, the ocular location of this device is still under discussion by experts.

The primary mirror reflects light from the celestial object to the main focus near the top of the tube, obviously if an observer put his eye there to observe with a modestly sized reflector he would block the light from the primary mirror with his head.

As expressed by the Isaac Newton Biography, this important scientist installed a small smooth mirror at an angle of 45 ° in the center of the main lamp and in this way brought the light to the side of the telescope pipe, the amount of light degenerated by this means is very small when compared With the full light-gathering power of the primary mirror, the Newtonian reflector is notorious among fanatic telescope builders.

A further variety of reflector was invented by another of Newton's contemporaries, the Scottish astronomer James Gregory. He placed a concave secondary mirror outside the primary focus to reflect light through a hole in the primary mirror. It is remarkable that the Gregorian design was adopted for the Earth-orbiting space observatory in 1980.

catadioptric telescopes

They are a special type of reflecting telescope where light first passes through a curved lens at the top of the telescope tube before reaching the primary mirror.

A catadioptric telescope is an optical method that is made to originate images of objects at an infinite distance and in turn brings refractive type optics (lenses) and reflective optics (mirrors).

The use of both mirror and lens optics produces certain benefits in terms of performance as well as in the manufacturing process. The term "catadioptric" is the union of two words: "catoptric" which has to do with an optical telescope that uses curved mirrors and "dioptric" refers to a telescope that uses lenses.

The four catadioptric telescope designs most used by amateur astronomers are:

  • Schmidt–Cassegrain
  • Maksutov–Cassegrain
  • Schmidt-Astrograph
  • Schmidt–Newtonian

Schmidt–Cassegrain telescope

The Schmidt-Cassegrain telescope has become one of the most notorious telescopes provided to the general public for many years, at its normal pace it consists of a small tube with a concave spherical primary mirror, a full-spread inspector lens, and a secondary mirror. highlighted which is smaller and located on the visual axis near the center of the sensor plate.

Maksutov–Cassegrain telescope

The Maksutov-Cassegrain telescope likewise is a very striking confection which is presented to enthusiastic astronomers, in its frequent distribution, this prestigious telescope possesses a short tube with a spherical concave main mirror, a full boot supervisory lens which is a flimsy negative foil lens and a supplemental mirror inside the corrector plate. 

Schmidt-Astrograph Telescope

The catadioptric astrograph is a telescope created to do astrophotography, these astronomical telescopes They don't have much to do with visualization, in tilted astronomy, astrographs are used mostly to get pictures of different things, but they have also been used to study the sky, as well as to look for comets or asteroids. 

Apart from its specific visual form, the astrograph usually has similar things, such as a low focal ratio, that is, shorter optical paths than other telescopes, and a wide field of focus that shows sharp portraits.

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Schmidt-Newtonian telescope

Schmidt-Newtonian telescopes are a meeting between the usual Newtonian reflecting telescope and a Schmidt-corrected Cassegrain, they make the photo on one side of the duct, closer to the front opening like the Newtonian, they have a sunken round primary mirror and a spherical corrector lens located near the entrance slit of the telescope duct.

What is the best beginner telescope?

Buying a telescope is an important first step towards a new level of appreciation of the night sky and the wonders found within it, there is an overwhelming number of telescope options. 

Of the best telescopes in use today, the best option is the reflecting telescope. This well-constructed aluminum telescope is a great mid-range option that will suit users at most levels. 

Telescope care and maintenance

It should have a good storage place that should be dry, dust-free, secure, and large enough for the telescope to go in and out easily. Ideally, you should keep your telescope at or near outside temperature. Doing so reduces the cooling (or heating) time required when set to night.

If your telescope or binoculars come with a case, use it, a case will not only add a second dust seal, it will also protect the instrument from accidental knocks.

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Consider cleaning a lens only when stains are evident; otherwise you can leave it like that, never clean a lens or a mirror just for the sake of cleaning it, because every time you touch it you risk damaging it.

Start the process by removing all the particles that have found their way to the surface, this does not mean blowing through the lens with your mouth; you'll just spit everywhere.

Many amateur astronomers prefer to use compressed air instead of a brush because nothing touches the surface, keep the can upright with the nozzle away from the lens at least as far as the manufacturer recommends. If the can is too close or tilted, it could hit the glass surface and stain it. 

Activities for astronomy enthusiasts

We run a series of workshops astronomy for local school teachers using activities of astronomy In a course we teach for elementary school students, school teachers give us feedback on successes and failures. 

Then we try the activities reviewed in the classroom. Through this in-service and pre-service feedback, activities of laboratory of astronomy in the course have been completely revised in the last three years. 


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